I can't seem to open the SCAR docs in the Essence Editor following the instructions from the knowledge center scripting guide. It's pretty hard to do much without the docs. Is there a way to fix this, or at very least is there another location I can go to read the docs? 

If you own a copy of Age of Empires IV you have access to those SCAR docs... also, some commands from CoH2's SCAR docs might work but with the engine overhaul I wouldn't count on it too much.

I have the same problem and validating the files does nothing

its a known issue since release, doubt its gonna change anytime soon

Was banging my head with old scardocs, but just found Janne252 (author of coh3-replay-enhancements and a one man army in CoH modding) generates its Scar types (for VS Code) from Age of Empires IV's Scardocs, which seem to be in sync with CoH3.  Kah-ching!  Find em in the repo: 

https://github.com/Janne252/coh3-scar-types/tree/master/generator/data/scardocs/html

Have you tryed to Create a scar file via mod?